Until the discovery of chiral activity, the development of electromagnetic radiation absorbing materials was limited to design variations in .epsilon..sub.r, (relative permittivity), and .mu..sub.r, (relative permeability) of the absorbing material. In order to match the impedance of the absorbing material to the free space impedance .epsilon. and .mu. are ideally equal. Practical considerations, however, dictate that this is not possible, with the result that the development of absorbers had been confined to searching for compromise combinations of .epsilon..sub.r and .mu..sub.r for the abosorbing material which produce the best results. There were therefore 2 degrees of freedom in choosing the properties of the absorber.
The introduction of chirality into an absorber produces an extra degree of freedom, expressed by the chirality parameter .beta., for the choice of properties of the abosrbing material.
Chirality is the handedness of an object, that is, the property of an object which renders it non-congruent with its mirror image. Work carried out on chiral absorbing materials indicates that electromagnetic radiation incident on an absorbing material containing chiral inclusions is caused to decompose into left-and right-circularly polarised forms and be scattered through the lossy dielectric material which is host to the chiral inclusions.